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Optical switches and switching architectures are used in optical networks for a variety of applications. One application of optical switches is in provisioning of light paths. In this application, the switches are used to form optical cross-connect architectures which can be readily reconfigured to support new light paths. In this application, the switches are replacements for manual fiber patch panels. As such, switches with millisecond switching times are acceptable. The challenge with respect to such applications is to realize large switch sizes.
At the heart of the optical switch is the switch core. In terms of switching function, switch cores may be characterized as either blocking or non-blocking architectures. A switch core architecture is said to be non-blocking if any unused input port can be connected to any unused output port. Thus a non-blocking switch core is capable of realizing every interconnection pattern between the inputs and the outputs. If some interconnection patterns cannot be realized, the switch is said to be blocking.
A popular architecture for building large non-integrated switch cores is the Spanke architecture illustrated in FIG. 1. In accordance with the Spanke architecture, an Nxc3x97N switch is made by combining N switches of the 1xc3x97N switch type along with N switches of the Nxc3x971 switch type, as illustrated. The Spanke architecture results in a strictly non-blocking switch core architecture that requires 2N switches. The switch illustrated in FIG. 1 is a 4xc3x974 switch core.
The increasing popularity of optical networks has resulted in the need for larger optical switch cores, thereby increasing the number of input and output channels (N). Since, in accordance with the formula above, the total number of switches used as well as the size of each switch in the Spanke switch core architecture increases substantially as the number of input and output channels increases, the cost of providing a large switch is significant and, in some instances, prohibitive.
The present inventors have recognized the reciprocal nature of the connections in a typical optical switch core employed in a conventional optical network. These reciprocity conditions have been used by the present inventors to provide a strictly non-blocking optical switch core architecture that significantly reduces the number of switches that are required to construct the switch core.
A switch core is set forth that comprises a plurality of duplex switches that are interconnected with an interconnection fabric to implement, for example, strictly non-blocking operation of the switch core for reciprocal traffic. In one embodiment, an N-way reciprocal switch is implemented. The N-way reciprocal switch comprises a plurality of duplex switches numbering N of at least a 1xc3x97(Nxe2x88x921) switch type (e.g., the duplex switches have at least Nxe2x88x921 ports available for connection to implement the interconnection fabric). The interconnection fabric interconnects the plurality of duplex switches so that each duplex switch is connected to every other duplex switch used in the interconnection fabric by a single connection. Such an architecture may also be used to implement a switch that is not strictly non-blocking.
In a second embodiment, an LM multi-stage reciprocal switch core having recursive properties and corresponding (n,m)-way switches are set forth. The LM multi-stage reciprocal switch core is comprised of a plurality of M-way reciprocal switches numbering at least 2Lxe2x88x921. Each of the plurality of M-way reciprocal switches is implemented as an N-way reciprocal switch described above, where N=M. A plurality of (L,2Lxe2x88x921)-way reciprocal switches numbering M are also used. The multi-stage LM reciprocal switch is itself an LM-way reciprocal switch that can be used to recursively build larger switches. For example, the LM reciprocal core switch can be used to implement a larger L1M1 multi-stage switch in which M1=LM. Altematively, or in addition, the M-way switches used to build the LM switch core can also be multi-stage in nature and built from smaller recursive components; i.e., from (j2jxe2x88x921)-way switches and (M/j)-way switches.